js: Name all the timeouts and idles

With very uninventive names. Names now, good names later.

https://bugzilla.gnome.org/show_bug.cgi?id=727983

js/ui/endSessionDialog.js

@@ -551,6 +551,7 @@ const EndSessionDialog = new Lang.Class({
 
                 return GLib.SOURCE_REMOVE;
             }));
+        GLib.Source.set_name_by_id(this._timerId, '[gnome-shell] this._confirm');
     },
 
     _stopTimer: function() {